You could ask why mercruiser used the high swirl head engine and claimed 260hp while Chevrolet pickups with fuel injection (granted it was tbi) only made 200? When they switched from high swirl to vortec the trucks picked up 60hp (and a better FI system), but mercruiser only claimed a 10-15 hp increase? Trucks and boats both got roller cams with the switch to vortec as well. They went from the worst performing small block heads ever made, to some of the best and yet no noticeable power gain. I?ve driven both the tbi trucks and the vortecs. There?s a huge difference.
A lot of the discrepancies in outputs are due to hp ratings. When many of these engines were first made, the were measured under the SAE Gross standard. The standard was updated in the 80s to SAE net.
If you look at the gmpp catalog, their cheapest old school 2-piece rear main small block is purported to make 300 hp with little more than a 600 or 750cfm carb. This is a late 70s, early 80s engine after everything was neutered for unleaded gas. I had a 78 Chevy truck with this engine that was factory rated at 265hp. Ain?t no way that thing was making that. We sold that truck in ?96 with less than 100k miles on the clock. The engine was good and tight. 265hp was a pipe dream.
We all know the marine industry lags years behind the car industry. I imagine many of the hp numbers are arbitrarily pulled from the arses of marketing and engineering departments to appease insurance companies and boat builders.
The vortec 4.3 2-barrel makes 190, and the 4 barrel makes 220-225. Ironically, vortec 5.7 uses the same carbs as the 4.3 albeit with different calibration kits.
